Epoxy resins as adhesives for bonding polyurethane to metal



Edited rates Fatent 3,042,545 Patented July 3, 1962 time This inventionrelates to epoxy adhesives and more particularly to the use of epoxyadhesives to bond urethane polymers to a metal surface.

Many applications of polyurethane elastomers demand high degree ofadhesion between polyurethane and a metal surface. This is particularlydesirable where polyurethanes are used which are cast from a liquidintermediate. The use of liquid polyurethanes or polyisocyanates inintermediate states of cure as adhesives in specialized laminates iswell-known in the art. The isocyanates may be used in either the form ofcement or as liquid pourable elastomer intermediate. It has been foundthat even molded or sheet polyurethane possesses a unique adhesion toother elastomeric or resinous materials. A large number of uses forthese adhesives and laminates has developed in the electrical, ship,aircraft, building and other industries which require high strengthdielectric materials. It has been found however that neither partiallycured polyurethanes nor liquid intermediates containing unreactedisocyanate groups have suificient adhesion to metals to be of widecommercial utility. Thus, when any stress is put upon themetal-polyurethane interface, the basic adhesion of the laminate bond isnot of a sufiicient quantity to be serviceable.

It is therefore an object of this invention to provide a method foradhering polyurethane resins to metal surfaces.

It is a further object of this invention to adhere liquid intermediatesof polyurethane possessing unreacted iso cyanate groups to a metalsurface.

It is a still further object of this invention to provide a method foradhering a polyurethane resin to a metal surface to form a bond having abond strength of at least 80 lbs. per inch at a static 90 pull.

It is a specific object of this invention to provide a method of using a1,2-epoxy resin adhesive for bonding polyurethane resinous materials toa metal surface.

It is a more specific object of this invention to provide a method foradhering a liquid polyurethane intermediate containing unreactedisocyanate groups to a metal surface using a 1,2-polyepoxide adhesive.

It is still a more specific object of this invention to provide a methodof adhering a polyurethane resinous material to a metal using a1,2-polyepoxide adhesive by substantially simultaneously curing thepolyurethane and the 1,2-polyepoXide to the metal surface.

It is a further specific object of this invention to provide a methodfor adhering a polyurethane resinous material to a metal by providing aninterlocking fused adhesive bond of a 1,2-polyepoxide and polyurethane.

It is a still further specific object of this invention to provide amethod for adhering a polyurethane resinous material to a metal byproviding an interlocking fused adhesive bond of polyurethane and acritical amount of a 1,2-polyepoXide to form a bond having a bondstrength of at least 80 lbs. per inch at a static 90 pull.

It is a primary object of this invention to provide alaminated structureof a polyurethane foam with a metal.

It is a further principal object of this invention to provide alaminated structure of a polyurethane foam with a metal using a1,2-p0lyepoxide adhesive.

It is a still further principal object of this invention to provide amethod for adhering a polyurethane foam to a metal by providing aninterlocking fused adhesive bond of polyurethane and a critical amountof a 1,2-polyepoxide to form a bond having high bond strength.

It has been found possible according to this invention to produce alaminated structure of urethane polymer and metal with an adhesive of a1,2-polyepoxide interposed between said metal and urethane polymer witha thickness of at least .023 gram per square inch of metal surface said1,2-polyepoxide and said urethane polymer having molecular bondsmutually penetrating the respective surfaces of the urethane polymer andthe 1,2-polyepoxide and having a bond strength of at least lbs. per inchat a static pull. It has further been found possible to provide a methodaccording to this invention for adhering resin having a film thicknessof at least .023 gram per square inch of metal surface and adhering apolyisocyanate elastomer to said 1,2-p0lyepoxide resin, saidpolyisocyanate elastomer and said 1,2-polyepoXide being characterized byan incomplete state of cure and curing the 1,2-polyepoxide resin andpolyisocyanate after a mutual bonding has occurred at the surfaceinterface of the 1,2- polyepoxide and the polyisocyanate polymer to forma bond having a bond strength of at least 80 lbs. per inch at a static90 pull.

More specifically this invention contemplates adhering a liquidintermediate of an incompletely cured polyurethane elastomer havingunreacted isocyanate groups or a very soft deformable polyurethanematerial having reactive groups and film Wetting properties to a metalsurface having an uncured or partially cured 1,2-polyepoxide with a filmthickness of at least .023 gram. per square inch of metal surface andco-curing or reacting the polyurethane and 1,2-polyepoxide to form alaminate bond having an increased bond strength whenever considerablestress is applied to the polyurethane-metal interface during service.

The necessary and preferred minimum bond strength for the purposes ofthis invention is at least 80 pounds per inch at a 90 static pull.

In order to produce the novel results of this invention it is necessarythat neither one of the polyurethane elastomeric intermediate or the1,2-polyepoxide curebefore a minimum mutual diffusion occurs at thesurface interface of the polyurethane and 1,2-polyepoxide. It has beenfound that a minimum film thickness of at least 0.023 inch of1,2-polyepoxide is necessary in order to ensure a minimum diffusion ofthe adhesive into the resinous material while maintaining a sulficientamount of 1,2-polyepoxide at the metal surface for bonding.

Any polyurethane which is thermoplastic and fluid and possesses activeisocyanate and curative amine groups may be adhered to any metal withany fluid epoxy resin containing 1,2-epoxide groups and preferably somecurative amine groups. In all such cases the bond strength ob tained isgreater than if no epoxy resin adhesive is used. This is quitesurprising since it is well known in the polyurethane art that thepresence of chemicals reactive with isocyanates are deleterious to thecured properties of these elastomers unless the molar ratios ofisocyanate are adjusted to compensate for their presence. Thepolyurethan elastomer-1,2-polyepoxide laminates are most effective wheremaximum interaction can take place between the two laminae. It ispreferred according to this invention to form bonds between thepolyurethane elastomer and epoxide resin Where the interaction issufficient 3 4 to obtain a bondstrength of 80 pounds per inch width of(II) Polyester derived polyurethanes, and in particumetal. Sucha bond isnecessary in practice-where the lar the diacid-glycol polyesters whichare reacted -with bond is under stress to any extent. To obtain a highdearomatic diisocyanates such as toluene diisocyanate, or gree ofinteraction, diffusion of the epoxy resin and polydiphenylmethane4,4'-diisocyanate. Typical diacids which urethane-phases into eachother-must be accomplished 5 may be used to form polyesters includeadipic acid, sebefore either phase hascompletely cured; thus thefasterbacic acid, azelaic acid, succinic acid and dilinoleic acid; thecurerate'the-faster diffusion must take place. The typical glycols includeethylene glycol, propylene glycol, cure rate is dependent upon thespecific reactants used tetrarnethylene glycol and hexamethylene glycol.The and the temperature of lamination and cure. The difformation of aprepolymer of a polyester derived polyfusion rate dependsupon themutual'solubility of the reurethane of the reaction product of an adipicacid ethylactants, the temperature of lamination and cure, and the oneglycol polyester and toluene diisocyanate is illustrated 'pres'sureonthesystem. The mutual solubility in turn by the following equation:

N00 o 0 Bio (CH2)r-O- OHzl %-O (CHg)z OH 2ooNoHt L j J:

ITTCO O O O O ITTCO -l| II I ll i CH3 NO-O(CH2)2O (CH2)4OCO (CH2)2O' -NCH;; C) H L .1.

will depend upon the nature of the reactants and, in the (III) Polyetherderived polyurethanes, and in particcase of the polymeric reactants,their molecular weight ular the reaction products of polyethyleneglycol,poly- "and structure. No quantitative picture can be given whichtetramethylene glycol or polypropylene glycol with arocorrelates all ofthese variables. However, those skilled matic diisocyanates such as2,4-toluene diisocyanate or in the art with the foreknowledge of thisinvention and diphenylmethane 4,4-diisocyanate. The formation of a theprinciples involved herein can quickly and qualitativeprepolymer fromthe reaction of polyethylene glycol ly determine the preferredelastomers and resins to use in and diphenylmethane 4,4-diisocyanate isillustrated by order to achieve optimum bond strengths. the followingequation:

Representative of the polyisocyanate intermediates and The preferredpolyurethane intermediates which may polyurethanes in an intermediatestate of'cure which can be used in the process of this invention arederived from be used according to this invention-are: the reactionproducts of 2,4-toluene diisocyanate or di- (I) The castor oil derivedpolyurethanes, especially phenylmethane diisocyanate with polyesterssuch as polythose derived from the reaction of castor oil with aromaticethylene adipates, polytetramethylerre adipates, polydiisocyanates suchas toluene diisocyanate or diphenyl- -ethyler1e sebacates or mixedpolyesters such as 80/20 methane 4,4-diisocya-nate. The formation of aliquid polyethylene-propylene adipate 'and 60/40polyethyleneintermediate polyurethane having unreacted isocyanatetetrarnethylene adipate containing hydroxyl end groups groups or aprepolymer of toluene diisocyanate with and'of a molecular weight ofapproximately 2000. Comcaster oil is represented by the followingtypical equation: mercial liquid polyisocyanate intermediates of theabove mixtures are sold under various trade names. The inii termediatesknown as Adiprene L'and Vibrath-ane' 6001,

. 6002, and 60-04 have been particularly useful in the p I 0 19 practiceof this invention.

g toggfmralio of isocyanate to polyester or polyether used it e liquidporyrsocyanate intermediates may vary N (0395050 over a wide range. Itis necessary that the number of OH20 (CHz)7CH=CHCHrCH--OH equivalents ofisocyanate exceed the number of equiva (CH) CH lents of reactivematerials in order to obtain resins having unreacted rsocyanate groups.The preferred mole ratio N00 or equivalent ratio is about 1.2 to about3.0 moles of I I isocyanate per mole of polyester or polyeth'ers. Astill 3OCN-O-CH3 more preferred range is to use from about 1.4 to about2.6 moles of isocyanate per mole of polyester or poly- ,O 0 IITCO ether.Polyurethane foams are utilized according -tothe I n process of thisinvention by adding appropriate foaming CH2-0-C-(CH2)7-CH=CH-CH2CHOCNHCCH3 agents such as water to thepolyurethane resinous mate- (CHDBCHBrials. Alternately, the polyurethane elastomer may be O O ITTCO whippedin air to produce foaming. Thenature of the H resulting foam will dependon the quantity'of foaming CHOC(C z)1- -C 2 C --Q 3 agent used, theviscosity of the polyurethane and the use (01.19603, of surface activeagents.

0 0 IYTCO A number of curatives are known forcuring polyi H H urethaneelastomers. Enhanced adhesion, however, -ac- *O cording to the processof this invention has been found 1195911, to be produced by usingamine'containing curatives. Ex-

amples of such amine curing agents are well known in the art.Representative of this class of compounds are the aliphatic and aromaticamines, beta amino alcohols etc. Amines which have been found that givepreferred results according to the process of this invention are3,3-dichloro-4,4'-diamino diphenylmethane, 3,3-dichloro- 4,4-diaminodiphenyl and ethanol amine. The curative may be added as a separatechemical compound or be built into the polyurethane. Examples of thelatter class of polyurethanes are the self curing" polyurethanes. Thepolyurethane systems of this invention are uncured or partially curedintermediates that still are thermoplastic and flow into curing forms.Curing of the polyurethane is usually carried out by the application ofheat. It has been found that, ordinarily, pressure curing isunsatisfactory. High pressure on the laminate bond increases diffusionof the 1,2-polyepoxide into the polyurethane at the surface interface toa point detrimental to the bond. However, in given cases it has beenfound to be practical to use a pressure cure although it does not giveas good a result as a heat cure carried out in a simple closed mold.

Any 1,2-epoxide resin has been found to be applicable as an adhesive toproduce the novel results of this invention. Generally the1,2-polyepoxides which are useful in this invention are obtained by thereaction of phenolic compounds with epichlorohydrin in the presence of abase. The resulting resins may be either bifunctional, trifunctional oritetr'afunctional. Representative phenols which may be reacted withepichlorohydrin to obtain 1,2-polyepoxides which are useful in thisinvention include bisphenol A, tetrachlorobisphenol A, diphenolic acid,novolaks, cashew phenols and aliphatic diols and triols. Intermediatedegrees of polymerization may characterize the 1,2-polyepoxide, such aswhen the epoxide chains have multiple functional groups which mayinteract to produce longer functional chains. Other representativeexamples of 1,2-polyepoxides which may be used are described in EpoxyResins by Irving Skicst, Reinhold Publishing Corp, 1958 and in US.Patents 2,699,402, 2,615,007 and 2,585,115. The 1,2-polyepoxide may beeither a liquid or solid. If a solid 1,2-epoxide resin is used it isdesirable to dissolve it in a suitable solvent. The concentration of1,2-epoxide resin in the solvent has a definite effect on the adhesiveproduced between the polyurethane and the metal surface. This ispresumed to be due to the wetting and film-forming properties of thedifferent viscosity levels which are obtained from differentconcentrations. The Wetting and film forming properties will also varywith the chemical structure and molecular weight of the 1,2-epoxideresins. Other 1,2-polyepoxides which have been found to be use ful asadhesives in this invention may be formed by the epoxidation ofcompounds containing unsaturated olefinic bonds, such as the epoxidationsynthetic rubbers with peracids.

Any curing agent useful in curing 1,2-polyepoxides may be used in curingthe 1,2-epoxide adhesives of this invention. The cure may be carried outin either a one stage or two stage cure. The preferred class of curingagents are polyfuuctional amines. Representative of this class of curingagents are ethylenediamine, diethylenetriamine, triethylenetetramine,tetraethylenepentamine, dicyandiamide, piperidine, N-(hydroxyethyl)diethylenetriamine, primary and secondary aliphatic and aromatic amines,and hydroxylamines. The amount of curing agent which may be employed inthe 1,2-polyepoxide resin is not critical and will depend on the natureof the 1,2-polyepoxide and the curative. The optimum ratio of curativeto 1,2-epoxide resin has been found to be 6 to 10 parts curing agent perhundred parts resin based on equivalent weights. In particular casesself curing 1,2-polyepoxides may be used advantageously as adhesives, inwhich the curatives are built into the 1,2-polyepoxide. Small amounts ofconventional fillers may be added to the 1,2-

6 polyepoxide adhesives to aid in distributing the bond stressthroughout the filler rather than limiting it to the glue line. Examplesof such fillers are well known in the art and include sand, silica,aluminum powder, graphite, asbestos etc.

The preferred enhanced adhesion of the polyurethane elastomericmaterials to metals is obtained by using a 1,2-polyepoxide having aminimum thickness of at least .023 gram per square inch of metal. Theminimum thickness has been determined on the basis of rates of diffusionof the polyurethane resinous material and. the 1,2- polyepoxideoccurring at the interface of the two laminae. The minimum amount of the1,2-polyepoxide film which is necessary to give a required adhesion ofpounds per inch width of polyurethane to metal has been determined to be.023 gram per square inch. If amounts lower than this are utilized ithas been found that the diffusion at the surface interface of thepolyurethane is so great that there is insufficient 1,2-polyepoxideremaining to effect the required bonding to the metal. The filmthickness is especially critical when pressure curing of the laminate isused since pressure increases the rate of diffusion at the surfaceinterface. The film thickness of the 1,2-polyepoxide may vary above .023gram per square inch of metal and still produce bonds having optimumstrength. The amount of 1,2-polyepoxide adhesive used depends on thenature of the metal, the 1,2-epoxide resin and polyurethane beinglaminated. However, it is essential, regardless of the laminatecomposition, to employ a 1,2-polyepoxide adhesive having a filmthickness of at least .023 gram per square inch to obtain a bond havingan adhesion of 80 pounds per inch width of metal. The basis of theenhanced bond strength obtained according to this invention is not fullyunderstood, however, it is thought that the diffusion occurring at the1,2-polyepoxide-polyurethane interface has two effects. First, thediifusion will give a wide graded interface rather than an abrupt glueline. The bond stress will thus be distributed throughout the bondingarea rathe than limited to the glue line. Second, the penetration allowscrosslinking bonds to form between the two resins as shown in (A) below.The cross-linking may occur in various ways depending on the nature ofthe polyurethane and 1,2-polyepoxide compositions. Thus the mutualdiffusion may cause bond formation by reaction of the 1,2-polyepoxidewith an isocyanate group as shown in (B) or by the reaction of theisocyanate with the 1,2-polyepoxide as shown in (C) o by the mutualreaction of both polyurethane and 1,2-polyepoxide with a curativederived from either system as shown in (D) R, R, R", and R may beorganic radicals in the above formulas and X may be either an organic orinorganic radical. The above reactions are diagrammatic and exemplaryonly and not definitive of all possible reactions that may occur at thesurface interface.

The rates of difiusion and the extent of diffusion of either thepolyurethane into the 1,2-polyepoxide or the 1,2-po1yepoxide into thepolyurethane Will depend on the nature of the respective compositions,i.e. molecular weight, viscosity and mutual solubility coefiicients. Therates of diffusion are critical to this invention only in that a minimum'dilfusion occurs before curing of the polyurethane and 1,2-polyepoxideresins occur.

Metals which may be laminated with a polyurethane according to thisinvention include iron, steel, aluminum, copper, brass, magnesium,titanium, etc. The adhesion of 1,2-polyepoxide to metals is well knownin the art and practically any metal may be utilized in the process ofthis invention. The 1,2-polyepoxide to be used as an adhesive in thisinvention is preferably one that is known to have high adhesion for theparticular metal used in the laminate.

The following specific examples are illustrative of the 8 EXAMPLE 2 Asecond method of cleaning steel or aluminum strips was as follows. Thestrip was immersed in liquid trichloroethylene followed by vapordegreasing with trichloroethylene for 30 seconds. The metal was thengrit blasted for 1 to 2 minutes with ground walnut shells. The surfacewas rinsed in tap water and dried in a forced draft oven at l150 F.

EXAMPLE 3 A liquid polyurethane resinous casting intermediate wassynthesized by reacting polytetramethylene ether glycol with2,4'-toluene diisocyanate. 3,3'-dichloro-4,4- diamino diphenylmethanewas added to the polyurethane intermediate as a curative. A1,2-polyepoxide resin consisting of 20% adhesive solids in a 2:1benzene-acetone solvent was applied to a 1 x 1 inch area of a 1 x 3 inchmetal plate cleaned according to the second procedure given above. Theabove pre-mixed liquid polyurethane casting intermediate was appliedwhile still pourable over the 1,2-polyepoxide and the laminate structurecured in an oven and thereafter aged. The results are summarized belowin Table I using different 1,2-epoxide resins.

Epon 1004 has a melting point of 95105 C. and an epoxide equivalent of870l025.

details of the invention. 'It is to be understood that the invention isnot limited to the details set forth therein.

The adhesion of a polyurethane to a metal surface was tested in thefollowing manner. A l x 1 square inch area of a cleaned 1 x 3 inch metalplate was covered with an 1,2-polyepoxide resin formulation so that aminimum weight of .023 gram of 1,2-polyepoxide res-in per square incharea was deposited on the metal. A polyurethane liquid intermediatecontaining the amine curative was cast on the plate over the 1,2-epoxideadhesive and sufiicient time allowed to permit at least a slightinter-dilfusion of molecules at the surface interface of the 1,2-ep0xideadhesive and the polyurethane. The laminated structure was then heatcured and aged according to standard processes. The adhesion of thecured polyurethane to the metal was tested by pulling the polyurethanefrom the metal plate at a 90 angle at a rate of two inches per minute,The results are recorded as pound pull per inch width.

EXAMPLE 1 A typical method of cleaning a steel strip for adhering1,2-polyepoxide and polyurethane laminae according to this invention wasas follows. The steel strip was washed with trichloroethylene, vapordegreased with tn'chloroethylene for 30 seconds and followed with a washin an alkaline detergent solution for 10 minutes at 160-180 C. The steelstrip was then washed with distilled water and dried in an oven at 200F. Following the drying, the cleaned steel was etched with sulfuric acidfollowed by a hydrofluoric-nitric acid solution. The etched steel wasthen rinsed in distilled water and dried in a 200 F. oven.

The above results show that the use of a 1,2-epoxide adhesive accordingto the process of this invention results in an increase in pounds pullfrom 32 without 1,2-polyepoxide to 109 using the epoxide resin.

EXAMPLE 4 The procedure of Example 3 was repeated substituting analuminum metal strip for the steel strip used in Example 3. The use of a1,2-epoxide adhesive of Epon 1004 with a 8% triethylenetetramine1,2-polyepoxide curative gave an adhesion value of 83 pounds pull perinch width of metal.

EXAMPLE 5 The procedure of Example 3 was repeated using apolytetramethylene ether glycol and 2,4-toluene diisocyanateintermediate and a curative of 3,3'-dichloro- 4,4-diaminodiphenyl. Theuse of a 1,2-polyepoxide of Epon 1004 with an 8% triethylenetetraminecurative gave an adhesion value of 98 pounds 'pull per inch width ofmetal.

EXAMPLE 6 Table 11 Percent Pound Laminate N 0. Metal Adhesive AdhesiveEpoxy Epoxy Pull Per Solvent Solids Resin Curative Inch Width None None17 Epon 100 do 38 Epon 1004 1 .do 61 Epon 1009 1 do 67 Epon 1004-.- 8%Triethylene- 06 tctrani'me Epon 100 None 54 Epon 1001 1 do 62 do 8%Triethylene- 88 tetramine do 4% Triethylene- 58 tetramine. Epon 1004 18% Triethylene- 86 tctramine. Epon 1007 1 do 86 Epon VI 8% Diethylene-80 triamine.

1 Epon resins are a commercial 1,2-epoxide resin sold by Shell Chemical60., and are based on the formula described in Example 3. Epon 1007 is asolid resin having a melting point of127-133" C. and an epoxideequivalent of 1550-2000. Epon 1001 has a melting point of 64-76 and anexpoxidc equivalent of 450-525. Epon 1009 has a melting point of 145-155and an epoxide equivalent of 2400-4000. Eponite 100 has a viscosity of0.9-

1.5 poises at 25 C. and an epoxide equivalent of 140-160.

EXAMPLE 7 The method of Example 3 was repeated using a polyurethaneobtained by reacting 4,4'-diphenylmethane diisocyanate with a polyesterof an 80/20 polyethylenepropylene adipate (average molecular weight2000) in a molar ratio of 2.0210

The polyurethane curative used in (a) was3,3'-dich1oro-4,4ldiaminodiphenylmethane and that used in (b) was3,3'-dichloro-4,4'-diaminodiphenyl.

Each of the above laminates gave polyurethane to metal bond strengths inexcess of 80.

The results are summarized below in Table III.

The example shows that when using an 1,2-epoxide resin adhesive having agram weight per square inch 30 duce a bond which has a preferredcommercial utility.

At .018 gram weight of resin per square inch of surface such a bond isnot obtained, whereas at .023 gram weight of resin per square inch ofsurface a bond is obtained having excellent commercial utility.

Table 111 Percent Pounds Epoxide Epoxide Pull Per Laminate No. MetalEpcxide Solvent Adhesive Resin Epoxide Gurative Inch Solids Width (a;Steel Benzene-Acetone 20 Epon 1000 None 150 (b do do 20 Epon 1004"- 8%Triethylene- 96 tetramine.

EXAMPLE 8 EXAMPLE The method of Example 3 was repeated using thepolyurethane of Example 6 in a molar ratio of 2.6:1.0 with a curative of3,3-dichloro-4,4'-diaminodiphenyl. Using an Epon 1004 epoxide resinadhesive at solids in a 2/ 1 acetone-benzene solvent with a 8%triethylenetetrarnine curative and a steel plate a bond strength ratingof 105 pounds per inch Width was obtained.

EXAMPLE 9 Table IV Grn. Wt. of Pounds Laminate No. Metal Resin/Sq. InchInch Surface Width The method of Example 9 was repeated using a 3,3-dichloro-4,4'-diaminodiphenyl curative for the polyureth- Having thusdescribed our invention, what we claim and desire to protect by LettersPatent is:

1. A process of bonding urethane polymers to metal surfaces with adegree of adhesion of at least pounds per inch at a static pullcomprising the steps of coating a metal surface with a layer of fluid,incompletely cured 1,2-epoxide resin containing from about 6 to about 10parts by weight of an amine curative per hundred parts of resin, saidlayer having a film thickness of at least 0.023 gram per square inch ofmetal surface, applying a lamina of fluid, incompletely curedpolyurethane prepolymer containing an amine curative upon said layer of1,2-epoxide resin, and subsequently fully co-curing said 1,2-epoxideresin and said polyurethane 75 prepolymer.

2. The process of claim 1 wherein the polyurethane prepolymer is formedby reacting an aromatic diisocyanate with a member selected from thegroup consisting of castor oil, diacidglycol polyesters and polyalkyleneglycol polyethers.

3. The process of claim 1 wherein the metal is selected from the groupconsisting of steel and aluminum.

4. A process of bonding urethane polymers to metal surfaces with adegree of adhesion of at least 80 pounds per inch at a static 90 pullcomprising the steps of coating a metal surface with a layer of fluid,incompletely cured 1,2-epoxide resin containing from about 6 to aboutparts by weight of a trialkylene-tetrarnine curative per hundred partsof resin, said layer having a film thickness of at least 0.023 gram persquare inch of metal surface, applying onto said layer of 1,2-epoxideresin a lamina of fluid, incompletely cured polyurethane prepolymercontaining as a curative a member selected from the group consisting of3,3-dichloro-4,4 -diaminodiphenyl and3,3-dichloro-4,4-diaminodiphenylmethane, I

said prepolymer being formed by reacting polytetramethylene ether glycolwith an aromatic diisocyanate, and subsequently fully co-curing said1,2-epoxide resin and said polyurethane prepolymer.

5. The process of claim 4 wherein the trialkylenetetramine curative isselected from the class consisting of trimethylenetetramine andtriethylenetetramine.

6. A process of bonding urethane polymers to metal surfaces with adegree of adhesion of at least 80 pounds per inch at a static 90 pullcomprising the steps of coating a metal surface with a layer of fluid,incompletely cured 1,2-epoxide resin containing from about 6 to about 10parts by weight of a trialkylenetetramine curative per hundred parts ofresin, said layer having a film thickness of at least 0.023 gram persquare inch of metal surface, applying a lamina of fluid, incompletelycured polyurethane prepolymer upon said layer of 1,2- epoxide resin,said prepolymer being formed by reacting a polyester consisting of an/20 mixture of polyethylene/propylene adipate and having an averagemolecular Weight of 2000 with an aromatic diisocyanate, and saidprepolymer containing as a curative a member selected from the groupconsisting of 3,3'-dichloro-4,4'-diamino diphenyl. and3,3'-dichloro-4,4f-diaminodiphenylmethane, and subsequently fullyco-curing said 1,2-epoxide resin and said polyurethane prepolymer.

References Cited in thefile of this patent UNITED STATES PATENTS OTHERREFERENCES Epoxy Resins (Lee and Neville), published by McGraw-Hill,pages 101 and 160.

Modern Plastics Encyclopedia for 1959, Foamed Polyurethanes, page 333f;note Molding Polyurethane at page 336.

1. A PROCESS OF BONDING URETHANE POLYMERS TO METAL SURFACES WITH ADEGREE OF ADHESION OF AT LEAST 80 POUNDS PER INCH AT A STATIC 90* PULLCOMPRISING THE STEPS OF COATING A METAL SURFACE WITH A LAYER OF FLUID,INCOMPLETELY CURED 1,2-EPOXIDE RESIN CONTAINING FROM ABOUT 6 TO ABOUT 10PARTS BY WEIGHT OF AN AMINE CURATIVE PER HUNDRED PARTS OF RESIN, SAIDLAYER HAVING A FILM THICKNESS OF AT LEAST 0.02O GRAM PER SQUARE INCH OFMETAL SURFACE, APPLYING A LAMINA OF FLUID, INCOMPLETELY CUREDPOLYURETHANE PREPOLYMER CONTAINING AN AMINE CURATIVE UPON SAID LAYER OF1,2-EPOXIDE RESIN AND SUBSEQUENTLY FULLY CO-CURING SAID 1,2-EPOXIDETESIN AND SAID POLYURETHANE PREPOLYMER.